1. Field of the Invention
The present invention relates to a method for driving a plasma display panel (PDP), and more particularly, to a method for driving a PDP with an automatic power control (APC) function for solving the problem of power shortage caused to a power source in a state where there are lots of light-on pixels in the PDP, that is, in a state where the brightness of the screen of the PDP is higher than a reference level, in an address-while-display (AWD) driving method in which addressing and sustaining are simultaneously active, and an apparatus thereof.
2. Description of the Related Art
A PDP is a display device for restoring image data input as an electrical signal with a plurality of discharge tubes arranged in a matrix to selectively emit light. PDPs are largely classified into direct current (DC) type PDPs and alternating current (AC) type PDPs according to whether the polarity of the voltage applied for sustaining a discharge changes or not over time.
FIG. 1 shows the basic structure of a general AC face discharge PDP. Referring to FIG. 1, a discharge space 15 is formed between a front glass substrate 11 and a rear glass substrate 17. In the AC face discharge PDP, a discharge sustaining electrode 12 is covered by a dielectric layer 13 so as to be electrically isolated from the discharge space 15. In this case, a discharge is sustained by the well-known wall charge effect. The above-described face discharge PDP includes two parallel discharge sustaining electrodes 12 on the front substrate 11 and an address electrode 16 on the rear substrate 17 and orthogonal to the discharge sustaining electrodes 12. According to this structure, an address discharge in which a pixel is selected occurs between the address electrode 16 and the discharge sustaining electrodes 12, and then a sustained discharge in which a video signal is displayed occurs between the two discharge sustaining electrodes 12, that is, a common (X) electrode 12a and a scanning (Y) electrode 12b. 
FIG. 2 is an exploded perspective view schematic illustrating a generally used AC three-electrode face discharge PDP, in which an address electrode 16 and a pair of discharge sustaining electrodes 12a and 12b perpendicular to the address electrode 16 are installed in each discharge space 15 which is divided by partitions 18 on a rear substrate 17. The partitions 18 block space charges and ultraviolet rays produced during a discharge to thus prevent cross talk from being generated at neighboring pixels as well as forming the discharge spaces 15. In order for a PDP to operate as a color display device, fluorescent material layers 19 made of a fluorescent material excited by the ultraviolet rays produced during discharge and producing red (R), green (G) and blue (B) visible light for displaying R, G and B colors, are repeatedly arranged in the discharge space 15 in order, thereby displaying R, G and B colors.
In order for a fluorescent-material-coated PDP to be capable of operating as a color video display device, a gray scale display must be utilized. Currently, a gray scale display method in which a picture of one frame is divided into a plurality of sub-fields driven in a time-division manner is widely used.
FIG. 3 shows a gray scale display method in a general AC PDP. As shown in FIG. 3, in the gray scale display method of a general AC PDP, a picture of one frame is divided into a plurality of sub-fields each consisting of address periods and sustained discharge periods. Here, a 6-bit gray scale implementation method, for example, is explained. A picture of a frame is temporally divided into six sub-fields and 64 (=26) gray scales are displayed. Each sub-field consists of address periods A1-A6 and sustained discharge periods S1-S6. Gray scales are displayed using a principle in which the comparative lengths of the sustained discharge periods are expressed visually in the brightness ratio. In other words, since the lengths of the sustained discharge periods S1 to S6 of the first sub-field (SF1) to the sixth sub-field (SF6) comply with a ratio of 1:2:4:8:16:32, altogether, 64 types of sustained discharge periods, that is, 0, 1(1T), 2(2T), 3(1T+2T), 4(4T), 5(1T+4T), 6(2T+4T), 7(1T+2T+4T), 8(8T), 9(1T+8T), 10(2T+8T), 11(3T+8T), 12(4T+8T), 13(1T+4T+8T), 14(2T+4T+8T), 15(1T+2T+4T+8T), 16(16T), 17(1T+16T), 18(2T+16T), . . . , 62(2T+4T+8T+16T+32T) and 63(1T+2T+4T+8T+16T+32T) are constituted, thereby displaying 64 gray scale levels. For example, in order to display a gray scale level of 6 at an arbitrary pixel, only the second sub-field (2T) and the third sub-field (4T) have to be addressed. Also, in order to display a gray scale level of 15, all of the first through fourth sub-fields have to be addressed.
FIG. 4 is a layout diagram of electrodes of an AC face discharge PDP constructed for implementation of the gray scale display method shown in FIG. 3. Here, among the discharge sustaining electrodes 12 consisting of paired horizontal electrodes, the electrodes connected in common are common electrodes (X-electrodes) 12a and the other side electrodes are scanning electrodes (Y-electrodes) 12b. The common electrodes (X-electrodes) 12a are all connected in common and a voltage signal having the same waveform, including a discharge sustain pulse, is applied thereto. Thus, a scanning signal of the discharge sustaining electrodes 12 is applied to the scanning electrodes, that is, the Y-electrodes 12b so that addressing is done between the Y-electrodes 12b and the address electrodes 6, and the discharge sustain pulse is applied between the Y-electrodes 12b and the X-electrodes 12a so that a display discharge is sustained. Waveforms of the driving signals applied to the respective electrodes connected as above are shown in FIG. 5.
FIG. 5 is a diagram showing the waveforms of driving signals of a generally used AC PDP, in which a picture display is implemented by an address/display separation (ADS) driving method. In FIG. 5, reference mark A denotes a driving signal applied to address electrodes, reference mark X denotes a driving signal applied to the common electrodes (to be also referred to as X-electrodes) 12a, and reference marks Y1 through Y480 denote driving signals applied to the respective Y-electrodes 12b. During a total erase period A11 a total erase pulse 22a is applied to the common (X) electrodes 12a for an accurate gray scale display to cause a strong discharge, thereby erasing wall charges generated by a previous discharge to promote the operation of the next sub-field (step 1). Next, during a total write period A12 and a total erase period A13, in order to reduce an address pulse voltage 21, a total write pulse 23 is applied to the Y-electrodes 12b and a total erase pulse 22b is applied to the X-electrodes 12a to cause a total write discharge and a total erase discharge, respectively, thereby controlling the amount of wall charges accumulated in the discharge space 15 (steps 2 and 3). Then, during an address period A14, data converted into an electrical signal is written on a selected location on the whole screen of the PDP by a selective discharge using the address pulse (data pulse) 21 and a write pulse 24 between the address electrode 16 and the scanning electrode 12b intersecting each other (step 4). Next, during a sustained discharge period S1, a display discharge, which is caused by continuously applying the discharge sustain pulse 25, is sustained for a given period of time, for the purpose of displaying picture data on the screen.
As shown, as the number of scanning lines increases, the time required for a write operation increases and the number of sub-fields increases so that the time allocated to the sustain discharge is reduced. Thus, a panel having a higher resolution has a lesser overall luminance. That is, for a high-resolution display, luminance degradation cannot be avoided.
FIG. 6 is a timing diagram illustrating an address-while-display (AWD) driving method. As shown in FIG. 6, erasing, writing and sustaining are performed at each sub-field while sustaining is being performed at another line or group. This can be done during the time between the application of successive discharge sustain pulses. Application of an erase pulse is also done in the same manner. The AWD driving method has an advantage in that it can attain a high luminance display. However, according to this method, many switching elements are necessary, the circuit for implementation of this method is complex and a stable discharge is hard to achieve. Also, much power is necessary for maintaining the brightness of the screen. Thus, a large power supply stage must be designed, which entails, however, the problem of an increase in size and cost. In particular, if a still-picture state is maintained for some time, like in a monitor, the service life of a PDP may be shortened. Thus, appropriate measures against the service life reduction problem must be taken.
According to the conventional ADS driving method, since the respective sub-fields are separate, the power shortage problem can be simply solved by stopping the application of discharge sustain pulses to the sub-fields during an automatic power control (APC) operation. In other words, while a discharge sustaining operation is performed over the entire screen, there is a way to reduce the number of sustained discharges at a ratio in each sub-field by outputting all the sustain pulses allocated to the sub-field and setting erase and reset periods at the end of the sub-field. At this time, the erase and reset periods invalidate the sustain pulses following an erase pulse in each sub-field so that the sustained discharges due to the invalidated sustain pulse is not generated.
However, according to the conventional AWD driving method in which a discharge sustain pulse is continuously applied, discharge sustain pulses of different sub-fields are applied to different lines. Thus, the application of discharge sustain pulses cannot be stopped at discretion.
To solve the above problems, it is a first object of the present invention to provide a method for driving a plasma display panel (PDP) by which automatic power control (APC) is allowed by discontinuing discharge by applying an erase pulse during the course of a sustained discharge.
It is a second object of the present invention to provide an apparatus for driving a plasma display panel (PDP) by which automatic power control (APC) is allowed by discontinuing discharge by applying an erase pulse during the course of a sustained discharge.
Accordingly, to achieve the above object, there is provided a method for driving a plasma display panel (PDP) with an automatic power control function, the PDP having discharge sustaining electrodes consisting of pairs of scanning lines and common lines, and address electrodes arranged orthogonally to the discharge sustaining electrodes, the respective electrodes being driven by an address-while-display (AWD) driving method in which addressing and sustaining discharge for expressing gray scale levels by sub-fields each consisting of an erase period, an address period and a sustained discharge period, are simultaneously performed at the scanning lines not in a time-division manner, to display a video signal of each frame on the PDP, the method comprising the step of applying erase pulses for invalidating some of discharge sustain pulses applied during the sustained discharge periods corresponding to the respective sub-fields so as not to cause a sustained discharge, at predetermined timing points during the sustained discharge periods of the respective sub-fields.
In the present invention, there is further provided the step of, before applying the erase pulses at predetermined timing points of the sustained discharge periods, determining application timing points of the erase pulses by obtaining an invalidation ratio of discharge sustain pulses applied to the respective sub-fields by detecting the power consumed at a power source stage for driving the PDP when the luminance is at the maximum peak.
Also, in the present invention, erase pulses having the opposite polarity to the discharge sustain pulses applied to the common lines may be applied to the common lines immediately after application of discharge sustain pulses applied to the common lines and have widths narrower than those of the discharge sustain pulses. Otherwise, erase pulses may be formed by reducing the width of one of the discharge sustain pulses applied to the scanning lines by a width corresponding to a predetermined period so as to be narrower than that of the discharge sustain pulses, by applying voltages lower than those of the discharge sustain pulses applied to the common lines, to the scanning lines in synchronization with the discharge sustain pulses applied to the common lines, or by applying pulse voltages having the opposite polarity to the discharge sustain pulses applied to the scanning lines, in synchronization with the discharge sustain pulses applied to the common lines.
Also, the voltage of each erase pulse is preferably greater than or equal to the difference between a discharge starting voltage and the voltage of each of the discharge sustain pulses applied to the common lines. Preferably, the application timing point of the erase pulse during the sustained discharge period is determined by a constant time ratio to be proportional to the periods of the respective sub-fields.
According to another aspect of the present invention, there is provided a method for driving a plasma display panel (PDP) with an automatic power control function, the PDP having discharge sustaining electrodes consisting of pairs of scanning lines and common lines, and address electrodes arranged orthogonally to the discharge sustaining electrodes, the respective electrodes being driven by an address-while-display (AWD) driving method in which addressing and sustaining discharge for expressing gray scale levels by sub-fields each consisting of an erase period, an address period and a sustained discharge period, are simultaneously performed at the scanning lines, not in a time-division manner, to display a video signal of each frame on the PDP, the method comprising the step of changing the application timing points of the erase pulses into predetermined timing points during the sustained discharge periods of the respective sub-fields, and applying the erase pulses during the sustained discharge periods, the erase pulses being applied for invalidating some of discharge sustain pulses applied during the sustained discharge periods corresponding to the respective sub-fields so as not to cause a sustained discharge.
In the present invention, there is further provided the step of, before changing the application timing points of the erase pulses and applying the same, determining the application timing points of the erase pulses during the sustained discharge periods of the respective sub-fields by obtaining an invalidation ratio of discharge sustain pulses applied to the respective sub-fields by detecting the power consumed at a power source stage for driving the PDP when the luminance is at the maximum peak.
Preferably, the erase pulses having the same polarity to the discharge sustain pulses applied to the scanning lines are applied to the scanning lines immediately after the application of discharge sustain pulses applied to the common lines and have widths narrower than those of the discharge sustain pulses.
Also, in the present invention, the erase pulses having the opposite polarity to the discharge sustain pulses applied to the common lines may be applied to the common lines immediately after the application of discharge sustain pulses applied to the common lines, and have widths narrower than those of the discharge sustain pulses. Otherwise, the erase pulses may be formed by reducing the width of one of the discharge sustain pulses applied to the scanning lines by a width corresponding to a predetermined period so as to be narrower than that of the discharge sustain pulses, by applying voltages lower than those of the discharge sustain pulses applied to the common lines to the scanning lines in synchronization with the discharge sustain pulses applied to the common lines, or by applying pulse voltages having the opposite polarity to the discharge sustain pulses applied to the scanning lines, in synchronization with the discharge sustain pulses applied to the common lines.
Here, the voltage of each erase pulse is preferably greater than or equal to the difference between a discharge starting voltage and the voltage of each of the discharge sustain pulses applied to the common lines. Also, the timing point of applying the erase pulse during the sustained discharge period may be determined by a constant time ratio to be proportional to the periods of the respective sub-fields.
To achieve the second object of the present invention, there is provided an apparatus for driving a plasma display panel (PDP) with an automatic power control function, the PDP having discharge sustaining electrodes consisting of pairs of scanning lines and common lines, and address electrodes arranged orthogonally to the discharge sustaining electrodes, the respective electrodes being driven by an address-while-display (AWD) driving method in which addressing and sustaining discharge for expressing gray scale levels by sub-fields each consisting of an erase period, an address period and a sustained discharge period, are simultaneously performed at the scanning lines, not in a time-division manner, to display a video signal of each frame on the PDP, the apparatus including a detection block for detecting data for the determination of timing points of applying erase pulses during sustained discharge periods of the respective sub-fields, the erase pulses being applied for invalidating some of discharge sustain pulses applied during the sustained discharge periods corresponding to the respective sub-fields, so as not to cause a sustained discharge, a logic block for determining application positions of the erase pulses by the data detected from the detection block, and blocks of driving scanning lines, common lines and address electrodes, for applying the erase pulses according to the logic determined by the logic blocks.
Alternatively, the present invention provides an apparatus for driving a plasma display panel (PDP) with an automatic power control function, the PDP having discharge sustaining electrodes consisting of pairs of scanning lines and common lines, and address electrodes arranged orthogonally to the discharge sustaining electrodes, the respective electrodes being driven by an address-while-display (AWD) driving method in which addressing and sustaining discharge for expressing gray scale levels by sub-fields, each consisting of an erase period, an address period and a sustained discharge period, are simultaneously performed at the scanning lines, not in a time-division manner, to display a video signal of each frame on the PDP, the apparatus including a detection block for detecting data for determination of changed timing points of applying erases pulses and applying the same during sustained discharge periods of the respective sub-fields, the erase pulses being applied for invalidating some of discharge sustain pulses applied during the sustained discharge periods corresponding to the respective sub-fields so as not to cause a sustained discharge, a logic block for determining changed application positions of the erase pulses by the data detected from the detection block, and blocks of driving scanning lines, common lines and address electrodes, for applying the erase pulses according to the logic determined by the logic blocks.